>>3131093My sightyly random guess is that Harpy biology expels unfertilized eggs(the cell) as an egg(shelled), avoiding messy human period/menstruation. However when fertilized the embryo grows like a normal human pregnancy, the developing embryo out growing the early unhardened shell, or the mothers body simply does not attempt to apply calcium layers to it, and then it gestates like normal.
Same for reptiles too I guess, not familiar with reptilian eggs.
